只允许3个实例的应用程序使用信号量 [英] Allow only 3 instances of an application using semaphores

问题描述

我正在尝试使用信号量来实现一个简单的例程，这将允许我只运行3个应用程序的实例。我可以使用3个互斥体，但这不是一个很好的方法，我试过这个到目前为止

I am trying to implement a simple routine using semaphores that will allow me to run only 3 instances of the application. I could use 3 mutexes but that is not a nice approach i tried this so far

var
  hSem:THandle;
begin
  hSem := CreateSemaphore(nil,3,3,'MySemp3');
  if hSem = 0 then
  begin
    ShowMessage('Application can be run only 3 times at once');
    Halt(1);
  end;

如何正确执行？

推荐答案

始终确保您释放信号量，因为如果您的应用程序死亡，则不会自动完成。

Always make sure that you release a semaphore because this is not done automatically if your application dies.

program Project72;

{$APPTYPE CONSOLE}

uses
  Windows,
  SysUtils;

var
  hSem: THandle;

begin
  try
    hSem := CreateSemaphore(nil, 3, 3, 'C15F8F92-2620-4F3C-B8EA-A27285F870DC/myApp');
    Win32Check(hSem <> 0);
    try
      if WaitForSingleObject(hSem, 0) <> WAIT_OBJECT_0 then
        Writeln('Cannot execute, 3 instances already running')
      else begin
        try
          // place your code here
          Writeln('Running, press Enter to stop ...');
          Readln;
        finally ReleaseSemaphore(hSem, 1, nil); end;
      end;
    finally CloseHandle(hSem); end;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

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